IPv6-RA autoconfiguration method allows to autoconfigure ipv6-capable
network interfaces by sending IPv6 prefixes throughout a link, so every
node that understands its message format can derive its own IPv6 address
based on internal algorithms. By using RA, you can configure almost any
node to serve as a router (i.e. running RADVD). As a matter of fact,
there are some flags in the RAs to set the DHCP as the "complement
device" to get full information about the network.
In cases when the only thing you need to know its a basic network
configuration (routes), or if devices don't need to use another external
services such as DNS, RA should me enough. On the other hand, DHCPv6
works in a way very similar like DHCPv4, and you can spread information
like the DNS-servers for a given link or network.
More advanced auto-configuration schemas may be reached if using
RA+DHCPv6. Think on scenarios like mobile networks, multihommed hosts
and low-power consuption ip based network-based networks.